The present invention disclosed herein relates to a power amplifier in a wireless communication terminal and system, and more particularly, to a mixed mode power amplifier with at least two operating modes.
This present invention is derived from researches accomplished as a part of IT R & D program of the Ministry of Information and Communication and Institution of Information Technology Association (MIC/IITA) [2005-S-017-03], Integrated development of ultra low power RF/HW/SW SoC.
According to the recent development of information communication technology, various contents such as movies, images, music contents, e-Books, etc are actively in service, based on a communication infrastructure of various forms such as high-speed internet, wireless internet, portable internet, terrestrial digital multimedia broadcasting (DMB), satellite DMB, etc. When considering a current technology development trend, the future mobile terminal can provide diverse services such as voice, internet, movie, and electronic signature/measurement/control, different from a typical voice based service. To realize those, complex functions and high transmission speed are required, and together with them, power consumption is one of the most important rising issues.
A power amplifier, a key component of signal transmission, is the most power consuming device in mobile communication terminals. By lowering the power consumption of the power amplifier in a mobile communication terminal and a mobile phone, multi-functions and complex functions of a low power consuming system can be realized. As a result, new mobile communication service industry can be revitalized, and thus each individual can enjoy services of various convenient functions through one terminal. Moreover, because it is possible for a user to enjoy multimedia communication for an extraordinarily long time, a leading information exchange society can be realized regardless of time and space. Accordingly, to maintain superior competitive power of a mobile terminal in a global market in an economic aspect and to create various additional services, a low power consuming component must be realized.
FIG. 1 is a block diagram of a typical mixed mode power amplifier.
Referring to FIG. 1, the power amplifier includes a high output amplifier unit 10 amplifying a radio frequency (RF) input signal, a mode switch 20 determining consumption current I1 and I2 of the high output amplifier unit 10, an input impedance-matching circuit 30 matching an input impedance of the high output amplifier unit 10, and an output impedance-matching circuit 40 matching an output impedance of the high output amplifier unit 10. The power amplifier of FIG. 1 is a mixed mode power amplifier capable of switching into a low output mode or a high output mode, an example of which is disclosed in U.S. Pat. No. 6,069,526 titled “PARTIAL OR COMPLETE AMPLIFIER BYPASS”, and filed on May 30, 2000 by Ballantyne.
Currently, the high-output amplifier 10 mainly uses one of a heterojunction bipolar transistor (HBT) array, a bipolar junction transistor (BJT) array, a field effect transistor (FET) array, and a complementary metal oxide semiconductor (CMOS) array. Generally, the typical power amplifier has very low power efficiency when an RF output power is less than a direct current (DC) consumption power. To resolve this limitation, as illustrated in FIG. 1, the mixed mode power amplifier operating in a high output mode or a low output mode according to the intensity of an output power has been suggested.
The consumption current I1 or I2 in the high or low output mode of the mixed mode power amplifier is determined by the mode switch 20. The consumption current I2 in the low output mode is lower than the consumption current I1 in the output mode. Generally, a supply voltage of the power amplifier is determined with a battery supply voltage (e.g., about 3.4 V to about 4.2 V in a case of a mobile phone). Accordingly, power consumption of the power amplifier is determined by an amount of the supply DC current.
When an RF input is enhanced in the high output amplifier 10, an RF power outputted from the high output amplifier 10 is increased together with the consumed DC current. At this point, a voltage swing width for generating the maximum output power is determined by a battery supply voltage level in the high output mode of about 1 W. In the high output power mode, a load impedance of about 2 Ohm to about 5 Ohm is used to adjust a current swing width. Compared to this, since the output power is low in the low output mode of about 16 dBm, instead of significantly increasing current consumption, the load impedance of more than about 15 Ohm is used to allow a RF voltage swing size to approach a battery supply voltage width. Therefore, the power efficiency can be improved.
If the output impedance between the high output mode and the low output mode of the power amplifier is identically shared, first in order to meet the maximum output requirement of the mobile phone, the load impedance needs to be sufficient to the high output mode. Accordingly, even if the consumption current I1 and I2 of the operating point in the high and low output modes changes through the mode switching, due to the limitation of the load impedance, the efficiency in the low output mode of less than about 16 dBm may not be more than about 10%. In this case, if the consumption current I1 and I2 in the two modes is decreased gradually, the efficiency may increase. On the other hand, characteristics of the non-linearity occur in a signal operation of the high output mode. This deteriorates linearity of the power amplifier. Therefore, there is a limitation in realizing a power amplifier that is capable of maintaining high linearity and having high efficiency in the high and low output modes, only by simply changing the consumption current I1 and I2, i.e., a simple mode switching operation.
FIG. 2 is a graph of probability density functions according to outputs of a code division multiple access (CDMA) mobile communication terminal and mobile phone. The graph of FIG. 2 is listed in IEEE Radio Freq. Integr. Circuits (RFIC) Symp. Dig., pp. 429-432 of the dissertation titled “Average current reduction in (W) CDMA power amplifiers” by D. A. Teeter, E. T. Spears, H. Bui, H. Jiang, and D. Widay. The graph of FIG. 2 illustrates probability density according to outputs of mobile communication terminal and a mobile phone in urban and suburban areas.
Referring to FIG. 2, actual usage rates of a mobile communication terminal and a mobile phone is concentrated on a region (i.e., a low output mode region) where an output power is less than about 16 dBm. However, load impedance for the maximum efficiency of the voltage amplifier circuit is designed for the high output mode in order to satisfy the maximum output requirement. For that reason, the power efficiency is rather decreased in the low output mode with the highest actual usage rate.
Recently, to describe the efficiency improvement of the power amplifier in the system such as a mobile communication terminal and a mobile phone, a notion for the average power usage efficiency (APUE) is used. The APUE is defined by a ratio of the supplied DC power and the average output power as following Equation 1 and Equation 2.
                              η          USE                =                              <                          P                              OUT                ,                i                                      >                                <                          P                                                I                  ⁢                                                                          ⁢                  N                                ,                i                                      >                                              [                  Equation          ⁢                                          ⁢          1                ]                                          η          USE                =                                            ∑                              i                =                1                            M                        ⁢                                          pdf                ⁡                                  (                                      P                                          OUT                      ,                      i                                                        )                                            ·                              P                                  OUT                  ,                  i                                                                                        ∑                              i                =                1                            M                        ⁢                                          pdf                ⁡                                  (                                      P                                          OUT                      ,                      i                                                        )                                            ·                              I                                  C                  ,                  i                                            ·                              V                                  CC                  ,                  i                                                                                        [                  Equation          ⁢                                          ⁢          2                ]            where <POUT,i> and <PIN,i> represent an average RF output power and a supplied DC power consumption according to pdf of a power amplifier, respectively. Pdf represents a probability function value according to output as illustrated in FIG. 2.
Generally, the maximum output power represents the most important characteristic in the CDMA power amplifier. However, most of the amplifiers operate at a low output power (i.e., in a low output mode region) of about 0 dBm in an urban area as illustrated in FIG. 2. The probability of 28 dBm output power is about 0.2% and the probability of a low output level. e.g. 0 dBm output power, is more than 3%. The probability distribution function has a form similar to the Gaussian distribution curve. An integral value calculated by a pdf function up to 16 dBm is about 94%. Accordingly, to increase a battery usage time of a terminal, the efficiency of a power unit in a power amplifier needs to be increased in an area where usage frequency is statistically high.